This invention relates to door closures and more particularly to an electromagnetically braked regenerative door closure.
Pivoted or swinging door control device are frequently used where it is desired to provide an automatic closing of the door upon passage of an entrant. Such devices are commonly found in those areas where it is generally desired that the door remain closed. One type of such control device utilizes the energy expended during the opening of the door to store energy in a compression spring and upon the absence of an opening force, utilizes that stored energy to cause a reverse pivoting or swinging of the door to its closed position. In order to moderate the closing speed, retarding systems may be utilized.
Currently well known and developed retarding systems utilize an hydraulic or pneumatic chamber to which a piston seal is connected for movement through the chamber. One-way passages allow the piston to move in one direction relatively freely during door opening while other highly constrictive controlled flow passageways retard movement of the piston in the other direction during door closing. By connecting the piston to the door control device mechanism, a controlled closing movement can be effected. An example of such a door closure mechanism is found in U.S. Pat. No. 4,064,589, the teachings of which are incorporated herein by reference.
While devices of this type adequately fulfill the function of storing opening energy and controllably releasing that energy to cause a door to close in a moderated fashion, they are relatively expensive to manufacture requiring very close tolerances to assure the long life maintenance of a seal in the hydraulic or pneumatic chamber both at the piston, and for the chamber itself to prevent leakage.
There are a number of patents which disclose automatic door operators which use a d.c. motor both as a motor and a generator to provide opening force and closing retardation when the closing is being effected by energy stored in a spring. Such patents include U.S. Pat. Nos. 3,247,617; 3,457,674; 3,425,161; 4,220,051; and 4,333,270.
Generally in those patents it is disclosed that the motor is powered so that upon the activation of a switch such as a floor mat the motor will provide an opening force to overcome the force of the return spring, as well as providing sufficient force to swing the door itself opened. During closing movement the main spring provides the force for closing the door and the motor which is connected for rotation relative to the door both in the opening and closing modes, rotates and acts as a generator, generating power to be fed back into the motor to retard the closing speed. Generally it is disclosed that the closing speed is reduced even further as the door approaches the final few degrees of closing movement. Slip clutches are provided between the motor and the door to prevent burn out of the motor in the event that the door becomes blocked.
Although such devices provide a non-hydraulic, common pneumatic braking system which controls the release of the stored spring energy during the closing movement of the door, these devices do require a d.c. motor of a sufficiently large size to not only compress the return spring, but also to provide the necessary force to open the door itself. Since these door control devices have a connection to the door either directly at the pivot point of the door or very close thereto, the moment arm of the door from the point of connection to the outer swinging portion of the door requires a substantial additional force for providing the opening of the door.
It would, therefore, be an advance in the art to provide a non-hydraulic, non-pneumatic, relatively inexpensive braking system for controlling the release of the stored energy during the closing movement of the door wherein the braking system can be made very small.